Interferons (IFNs), including IFN-α, IFN-β, and IFN-γ, are natural proteins produced by immune cells in response to foreign agents (e.g., pathogens) or abnormal self agents (e.g., cancer cells). They have been widely used in treating viral infection and cancer.
Mature human IFN-α-2b (hIFN-α2b) and its counterparts in other species have two naturally-occurring disulfide bonds, which are crucial to their therapeutic applications. In hIFN-α2b, these two disulfide bonds are formed between Cys1-Cys98 and Cys29-Cys138, respectively. The former is required for the protein activity. Loss of the latter, on the other hand, renders the protein immunogenic.
hIFN-α2b is commonly prepared by expressing its encoding cDNA in E. coli. It has been found that the protein thus prepared contains a substantial amount of structural isoforms, including oligomers and slow monomers, both of which migrate slower than their native counterparts in SDS-polyacrymide gel electrophoresis under non-reducing conditions. These isoforms, resulting from formation of non-natural inter- or intra-molecular disulfide bonds, have no therapeutic value as they are either inactive or immunogenic. It is therefore highly desired to develop new techniques for producing IFN-α proteins with little isoform contamination.